Which is the best: steel, titanium, aluminium alloy or carbon? For that matter, what about bamboo and wood?!
Such questions have vexed bike designers for many decades. This post is not about the relative merits of each of these materials for bike frames, as there is plenty of information about that already (one of my favourite resources is here). Rather, I give my views on fitness for purpose and ride quality. I used to believe people who said that aluminium gives a harsh ride, until I bought a good alloy road bike, alloy front forks and thoroughly tested them in cyclocross. In my view, in practice, neither were harsh. I used to believe people who said the type of steel tubing really matters, and those who said 531C is the best, until I realised that it is not that simple. In the 1990s 7 steel bikes, identical except for the tubing, were built and blind tested (see this fascinating article). After much riding and reflection, the reviewer commented that the differences between the steel alloy bikes were very subtle - really rather minor.
There are many ways to create a bike that works well and suits its intended purpose. Factors such as weight, shape, stiffness, tyres and saddle have a huge impact to how a bike works and feels. Ride quality is determined by so much more than frame material. I think there is a good way to look at this. First of all, think of all the things that make a bike efficient. What makes it go further, faster for less work input by you, the engine?! Then list the things that make your life on the bike more comfortable. After doing that, note that some of the comfort enhancing aspects serve to reduce efficiency, but even so, the increase in comfort may be worth it. So here's what I mean:
1. Bearings smooth. To put it another way, a jammed wheel would give atrocious "ride quality"!
2. Stiffness. Frame doesn't flex around when you push the cranks, descend at speed or turn
3. Wheels don't wobble, hop, or flop
3. Tyres have low rolling resistance
4. A decent engine: rider has appropriate fitness and technique (my grandma ain't as efficient as Bradley Wiggins!)
5. Shape and size
6. Fitting is good, proper muscles engaged
7. Clipless pedals
8. Light weight
10. Components function efficiently
Some of which work against the following:
a. Tyre size and pressure - fatter, softer are more comfy
b. Saddle type
c. Suspension, whether through flexy frame or actual springs/dampers (which also add weight)
d. No nasty resonant effects - from high frequency teeth rattling vibrations, to scary front wheel shimmies
e. Relaxed seating position and rider view point
f. Contact points feel nice, allow subtle body shifts and position adjustments while riding
g. Components are convenient and comfortable to use
I hope you can see where the frame material fits into this. Basically, it contributes to 2, 8, a bit of 9, c and d. But any of the other factors could ruin the rider's experience of what is otherwise a great frame. Thus, all of the materials listed at the start of this article may be used to make a lovely bike frame that functions very well - but only under particular conditions. Heavier tubing will make a stiffer bike. Both the load lugging touring cyclist and the road racer want a light, stiff bike but suitable frames are not the same in each case. Carbon fibre is great until it gets whacked or even scratched, when a small defect could make it dangerous through risk of catastrophic failure. Bamboo is natural carbon fibre! Modern super-steel alloys like Reynolds 953 undoubtedly make light, comfortable, strong, stiff, corrosion resistant frames, but so can carbon fibre composite, titanium and aluminium alloys. To underline my point, last season, Zdenek Stybar and Ian Field (world and national cyclocross champions) both used aluminium alloy bikes, while many of their world class competitors opted for carbon frames, but I don't know of any champion racers who used a steel frame.
Ideally, your choice should be a personal one, based on real evidence and your preferences after test riding. After all, you will be riding the bike, not the person who gave their opinion on the frame material!